Most everyone has missed the point with these extensive medical exams.
Yes, the cruise lines want to ensure that you do not have a communicable disease that might contaminate passengers and crew.
Yes, the cruise lines want to ensure that you are basically fit and able to do your job - which includes safety duties where others must rely on your fitness.
But the biggest issue for the cruise lines is health insurance. Most cruise lines are self-insured. Crewmembers who are sick or injured on cruise ships receive free medical attention at cruise line expense. It is not unheard of for crewmembers to try to hide illnesses until they are hired and onboard, and then request the medical treatment that they could not or would not afford at home.
The cruise lines are trying to protect themselves from seriously ill people who are trying to get the job to avoid paying for very expensive medical care.